The disclosures of Japanese Patent Applications No. 2001-197269 filed on Jun. 28, 2001 and No. 2002-034769 filed on Feb. 13, 2002, each including the specification, drawings and abstract, are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an evaporated fuel processing apparatus for an internal combustion engine, and more particularly to an evaporated fuel processing apparatus adapted to purge evaporated fuel generated in a fuel tank into an intake passage of the internal combustion engine.
2. Description of Related Art
An evaporated fuel processing apparatus, such as that as disclosed in Japanese Laid-open Patent Publication No.7-54719, is known. The evaporated fuel processing apparatus uses a canister for trapping evaporated fuel (fuel vapors) generated in a fuel tank, and releases (purges) the fuel vapors stored in the canister into an intake passage of an internal combustion engine during an operation thereof. In the internal combustion engine including the evaporated fuel processing apparatus as described above, the quantity of air contained in purge gas (i.e., purge air quantity) is a useful parameter for controlling the quantity of purge gas flowing from the canister into the intake passage of the engine, and for controlling the fuel injection amount so as to reduce a deviation of the actual air-fuel ratio from a target air-fuel ratio.
For determining the quantity of the purge air, the above-described known evaporated fuel processing apparatus includes a dedicated airflow meter for detecting the quantity of air flowing into the canister. The airflow meter enables accurate detection of the quantity of air that passes through the canister, namely, the quantity of purge air contained in the purge gas that flows from the canister into the intake passage. Thus, the known evaporated fuel processing apparatus is able to accurately control the quantity of purge gas and the fuel injection amount by using the detected purge air quantity as a control parameter.
In the known evaporated fuel processing apparatus, however, a pressure loss occurs at the airflow meter disposed in an ambient air inlet of the canister. Such a pressure loss may cause a reduction in the purge gas quantity and may cause a change in the internal pressure of the canister in accordance with the change in the purge gas quantity. If the internal pressure of the canister changes, the quantity of fuel vapors purged from the canister changes accordingly, resulting in deterioration of the accuracy of purge control (air-fuel ratio feedback control).
Furthermore, when the airflow meter is exclusively used for detecting the quantity of purge air as described above, the cost of the evaporated fuel processing apparatus increases because of the use of the airflow meter as compared with the case where such an airflow meter is not used. Thus, the known evaporated fuel processing apparatus suffers from various problems caused by the use of the dedicated airflow meter.
It is therefore one object of the invention to provide an evaporated fuel processing apparatus that is able to detect a quantity of purge air flowing from a canister into an intake passage of the engine without using a dedicated airflow meter.
To accomplish the above and/or above object(s), there is provided according to one aspect of the invention, which provides an evaporated fuel processing apparatus for an internal combustion engine, which includes: (1) a canister that traps fuel vapors generated in a fuel tank, and (2) a purge control valve disposed between the canister and an intake passage of the internal combustion engine. A controller of the evaporated fuel processing apparatus determines (a) a quantity of purge gas that passes through the purge control valve, (b) a fuel injection amount correction coefficient for reducing a deviation of an actual air-fuel ratio from a target air-fuel ratio due to the purge gas, (c) a fresh air ratio that represents a ratio of purge air contained in the purge gas to the purge gas, based on the fuel injection amount correction coefficient, and (d) a quantity of the purge air based on the quantity of the purge gas and the fresh air ratio. The controller then controls the internal combustion engine based on the quantity of the purge air.
With the evaporated fuel processing apparatus constructed as described above, the rate of the purge air to the purge gas, or the fresh air ratio, is obtained based on the fuel injection amount correction coefficient, and the purge air quantity can be calculated based on the fresh air ratio. Thus, according to the above aspect of the invention, the purge air quantity can be determined without using a dedicated airflow meter, and the thus determined purge air quantity can be utilized for controlling the internal combustion engine.
According to another aspect of the invention, there is provided an evaporated fuel processing apparatus, which includes: (1) a canister that traps fuel vapors generated in a fuel tank, and (2) a purge control valve disposed between the canister and an intake passage of the internal combustion engine. A controller of the evaporated fuel processing apparatus determines (a) a quantity of purge gas that passes through the purge control valve, (b) a fuel injection amount correction coefficient for eliminating a deviation of an actual air-fuel ratio from a target air-fuel ratio due to the purge gas, (c) a quantity of fuel vapors supplied to the internal combustion engine through the purge control valve, based on a basic fuel injection amount and the fuel injection amount correction coefficient, and (d) a quantity of purge air that passes through the purge control valve, by subtracting the quantity of the fuel vapors from the quantity of the purge gas. The controller then controls the internal combustion engine based on the quantity of the purge air.
With the evaporated fuel processing apparatus constructed as described above, an amount of correction of the fuel injection amount can be obtained based on the basic fuel injection amount and the fuel injection amount correction coefficient. The correction amount corresponds to the quantity of fuel vapors purged from the canister. Thus, according to the above aspect of the invention, the quantity of fuel vapors purged can be obtained based on the basic fuel injection amount and the fuel injection amount correction coefficient. It is thus possible to determine the quantity of purge air with high accuracy, by subtracting the quantity of fuel vapors from the quantity of the purge gas.